1. Field of the Invention
The invention relates generally to improvements in power tools used in the installation of threaded fasteners and more particularly, to a quick-change socket and key retainer assembly for specialized threaded fasteners of the type used in aerospace and related industries.
2. Brief Statement of the Prior Art
A variety of specialized fasteners have been developed and are widely used in the aerospace and related industries. These specialized fasteners have been designed to meet specific design criteria for a variety of applications. One such fastener is currently in widespread use throughout the aerospace industry. The Hi-Lok® type fastener was developed by Hi-Shear Corporation and is manufactured under a variety of names. The Hi-Lok® type fastener is particularly adapted for fastening two or more metal panels or workpieces together where there is no access to the bolt head. That is, the fastener is designed to fit through a preformed opening in a substrate or workpiece with the bolt head inaccessible by the power tool used in the installation of the fastener.
The Hi-Lok® type frangible fastener includes two basic components, a bolt component which has a bolt or head end and a threaded end, and a collar component which has an internally threaded body portion and a torque limiting drive nut portion. Generally, a series of appropriately spaced holes are bored in the workpiece. One of the most important features of this fastener is that it enables the fasteners to be installed with the installation tooling disposed on one side of the workpiece assembly.
The bolt component is inserted from the opposite side of the panel assembly, that is, the side inaccessible to the power tooling. The body of the collar component of the fastener is then threaded a few turns onto the exposed threaded end of the bolt component from the accessible side of the workpiece assembly.
The power tooling that drives the fastener includes a rotary socket member which has a forwardly opening noncircular, preferably hex recess that engages the torque limiting drive nut portion of the collar component. In addition to the hex socket, the power tooling has a centrally located rotationally stationary noncircular, preferably hex key or hold bit which is adapted to snugly fit into a broached hex cavity located in the threaded end portion of the bolt component of the fastener. The rotary socket member is rotated by a powered motor in the power tool body, and threadedly drives the collar component of the threaded fastener down onto the bolt component until a predetermined torque preload on the workpiece assembly is reached. At the same time that the collar component is threaded onto the threaded bolt component the rotationally stationary noncircular or hex key or hold bit mounted to the broached hex cavity in the threaded shank of the bolt component holds the fastener against rotation. Upon reaching the predetermined torque limit, the drive nut portion of the collar component is automatically sheared from the threaded body of the collar component which then becomes the nut portion of the fastener. This unique feature avoids over-torquing the fastener as well as eliminates the need for manually monitoring the torque on the fastener.
A problem that continues to exist with this type of fastener installation tool is the tendency of the hex key or hold bit to twist or otherwise deform. Additionally, changing the hex key or hold bit after damage or after wear or to a different size key is a relatively slow procedure due to the various mechanisms proposed to prevent the hex key or hold bit from rotating relative to the fastener during installation of the nut.
The prior art proposes various power tools for the installation of Hi-Lok® type frangible fasteners. Zils, U.S. Pat. No. 4,462,281, discloses a straight drive type of tool wherein the socket and hex key approach the workpieces at right angles relative to the general plane of the workpieces. The Zils tool has the disadvantage that if the key is damaged or broken, disassembly of portions of the head assembly of the tool is required in order to remove and replace the hex key. It also has the disadvantage that the key may be difficult to remove because of sealant fouling, and a twisted hex key may not even be removable for replacement, or may damage the key holder, requiring almost complete disassembly of the tool head for removing the stuck key and its key holder. These disadvantages translate into substantial manual effort and tool downtime.
Bochman, U.S. Pat. No. 3,027,789, discloses a geared L-head-type tool that might be applicable to a Hi-Lok® type frangible fastener, although there is no mention of a frangible fastener in this patent. Replacement of the key would require disassembly of a sub-housing which houses an enlarged key head and key spring from the main tool head. This would require substantial manual effort and tool downtime.
Bosten, U.S. Pat. No. 3,584,527, discloses a power tool which, by its nature, could be applied to a Hi-Lok® type frangible fastener, although its stationary key has a Phillips screwdriver-type head. It is a straight, offset drive which would require substantial disassembly, and hence manual effort and tool downtime, to remove and replace the bit or key.
Bangerter et al., U.S. Pat. No. 3,323,394, discloses a straight drive power tool which is generally similar to the tools disclosed in both Bosten and Zils, but has a torque-limiting clutch associated with the bolt-restraining bar. As with both the Bosten and Zils devices, the Bangerter al. device would require substantial disassembly to remove and replace a broken bar or key, requiring substantial effort and downtime. The binding problem discussed in connection with Zils would also be equally applicable to Bosten and Bangerter et al.
Batten, U.S. Pat. Nos. 4,538,483 and 4,617,844, disclose what purports to be a ball detent type quick-release and replacement system for removal of a damaged or broken drive head of the tool. There are a number of drawbacks with the ball-detent type of retention systems. The key has to be manually pulled out of the front end of the holder which requires a separate gripping tool such as pliers. For removal and replacement of the hex key, the ball detent system requires that the key holder be pulled rearwardly against the force of the retention spring, and then a “flipper” or spacer block be pivoted under the head of the holder to bring the detent in the holder into axial registry with the internal annual groove in the socket member. The retention springs are sometimes so rigid as to require a special tool to pry them up in order to get the flippers underneath them.
Another problem with the ball detent retention system is that contamination entering the interface region between the hex key and the holder key way often prevents extraction of the key from the key holder.
Gauthreaux et al., U.S. Pat. No. 7,874,232, discloses a quick connect socket and hex key retainer assembly wherein a lever is slid in one direction to lock the retaining slide into locked position. When the retaining slide is moved into the locked position, the retaining slide slides into and engages an annular groove that is located around the circumference of the exterior surface of the drive shaft of the socket of the socket assembly. Once the retainer slide is engaged with the annular groove, the socket assembly is secured and engaged to the gear head of the fastening tool with a lock screw. In order to change a hex key the complete socket assembly must be removed and disassembled from the power tool.
There exists, therefore a need for further improvements in and to fastener installation tools of the type having a hex key or hold bit coaxially disposed within a power drive socket for engaging a hex cavity located in the threaded end portion of the bolt component of a Hi-Lok® style fastener, particularly with respect to providing a simplified quick connect or disconnect feature for replacing the hex key or hold bit member.